JP4316680B2 - High performance impulse ink ejection method and impulse ink ejection apparatus - Google Patents

Description

TECHNICAL FIELD This invention relates to drop-on-demand or impulse fluid ejection that ejects droplets of fluid, such as ink, in response to the energy of various forms of transducers.
Background Art Impulse fluid ejection or impulse ink ejection is designed and driven to eject droplets of fluid, such as ink, from a chamber through an orifice of an ink ejection device. In many applications, it is not necessary to operate the ink ejector with high performance, i.e., high speed and long range. However, many applications, including industrial applications, require high performance ink ejectors.
For example, in various industrial inkjet applications, the droplets can be removed from the inkjet orifice while the droplet size is kept relatively small to create a high resolution dot (dot) on the target. It is very important to eject the droplets at high speed and with a long range so as to reach the target at some distance. In order to do this, it is important that the head and tail of the droplets travel at a relatively fast, equal speed while being tied together.
In the prior art, it was difficult to increase the range at high speed. For example, an expansion type piezoelectric transducer of an ink jet print head of the type disclosed in US Pat. No. 4,646,106 uses a Helmholtz frequency of a fluid of 25 kHz to 50 kHz and a piezoelectric longitudinal vibration mode resonance frequency comparable thereto. High performance in terms of frequency response. However, the droplets that are formed have a long tail that can slow the speed of the droplets, and range is not the best performance.
U.S. Pat.No. 4,523,201 and U.S. Pat.No. 4,523,200 are similarly driven by a voltage waveform with a first long pulse and a second short pulse designed to quickly break the tail of the droplet. A print head is disclosed. However, the device disclosed herein is designed to operate at a Helmholtz frequency of 50 kHz or less, and generates harmonic frequencies that detach the tail to produce high speed droplets with improved range. The effect of is not disclosed. On the contrary, the aim of the second pulse is hardly improved.
Referring to FIGS. 1A-1F, FIG. 1A shows drive waveforms diagrammatically, and FIGS. 1B-1F show ink jet devices at various points in time. In FIG. 1A, the drive waveform is shown with voltage on the ordinate and time on the abscissa. At time A, as shown in FIG. 1B, the ink jet device is stationary and the transducer 10 is maintained with no voltage applied, and a predetermined amount of ink 12 is placed in the chamber behind the orifice 16. 14 At time B shown in FIG. 1A, the transducer 10 is driven by a voltage pulse 17 as shown, which shortens the length of the transducer 10 and therefore increases the amount of ink 12 in the chamber 14. The meniscus in the orifice 16 is drawn into the position.
As shown in FIG. 1C corresponding to time C in FIG. 1A, the converter 10 starts to expand when the voltage applied to the converter 10 decreases. As a result, a certain amount of ink 12 in chamber 14 begins to contract, causing meniscus 18 to advance through orifice 16 as shown in FIG. 1D. Slightly after time C and before time D, as shown in FIG. 1E, the transducer 10 returns to a substantially stationary state, as shown in FIG. Begins to form. In FIG. 1F, corresponding to time D in FIG. 1A, the droplet 20 travels some distance from the orifice 16 with a slow-tailing tail 22 associated with the droplet 20. As shown in FIG. 1F, the tail 22 is disconnected from the meniscus 18 of the orifice 16 before an amount of ink 12 in the chamber 14 returns to the state shown in FIG. 1B. As can be readily seen from FIG. 1F, assuming that the tail 22 and the head 20 remain connected during movement to the target, the tail 22 is stretched to create an “overcoat” state on the target. I will create it. The tail 22 moves relatively slowly compared to the speed of the head, which lengthens the tail 22 and divides the tail 22, thus reducing the total range distance to the target.
In prior art devices of the type disclosed in U.S. Pat. Characterized. The tail formed on the meniscus is subjected to a pressure disturbance of about 45 kHz. Therefore, the tail is disconnected as shown in FIG. 1F in response to this disturbance while the speed during the cycle is negative, thereby providing a very small acceleration component, so the head speed is fast and the tail speed is high. Slows down, so that the tail becomes longer beyond a long print gap, resulting in poor print quality.
DISCLOSURE OF THE INVENTION According to the present invention, a high-performance fluid ejection method and fluid ejection device in which high-speed droplets are ejected from a fluid ejection device are provided.
Furthermore, the present invention provides a high-performance fluid ejecting method and fluid ejecting apparatus in which a droplet has a long range.
The present invention further provides a method of operating an impulse fluid ejection device, the fluid jet device comprising a chamber, an orifice for ejecting a droplet from the chamber, and a transducer having a resonant frequency and a harmonic frequency. The method of operation comprises the step of generating an energy pulse of a width coupled to the transducer to cause a resonant frequency of the transducer. The droplet ejection is performed in response to one energy pulse so that the droplet has a head and a tail connected to the head. Another energy pulse of another width coupled to the transducer is generated that is substantially shorter than the one energy pulse to cause a harmonic frequency. The tail associated with the head is detached from the head of the droplet in response to another energy pulse. As a result, the head and the rest of the tail travel together toward the target.
In the preferred embodiment of the present invention, another pulse is generated after one pulse in time. In another preferred embodiment of the invention, another pulse is generated before one pulse in time.
According to another important feature of the invention, the fluid or ink droplet having a head and a tail attached to the head comprises at least 20 picoliters, preferably more than 60 picoliters. And preferably travels at a speed of at least 6 meters per second, more preferably has a moving distance or range of at least 6.4 mm (0.25 inches), preferably 12.7 mm (0.5 inches) or more. It is.
According to a further important feature of the invention, the transducer has a resonant frequency of 50 kHz or higher, preferably 75 kHz or higher and a harmonic frequency of 150 kHz or higher, preferably 200 kHz or higher.
According to another important feature of the invention, the fluid ejection chamber or ink ejection chamber is preferably a volume having a Helmholtz frequency of 50 kHz or higher.
In a preferred embodiment, the width of one pulse is not less than 5 microseconds and not more than 100 microseconds, and the width of another pulse is not less than 0.5 microseconds and not more than 6 microseconds. The delay time between one pulse and another pulse is not less than 1 microsecond and not more than 5 microseconds.
[Brief description of the drawings]
1A-1F are a diagram and partial schematic diagram of the prior art described above.
FIG. 2A is a waveform for driving a fluid ejecting apparatus or an ink ejecting apparatus according to a preferred embodiment of the present invention.
FIG. 2A 'is another waveform for driving a fluid ejection device or ink ejection device of another preferred embodiment of the present invention.
FIG. 2B is a partial schematic diagram of the fluid ejection device or ink ejection device of the present invention driven by the waveform of FIG. 2A or 2A ′, showing when a droplet emerges from the ink ejection device.
FIG. 2C is a partial schematic diagram of a fluid ejection device or ink ejection device, showing the device of FIG. 2B after a slight amount of time.
FIG. 3 is a partial schematic / block diagram of a jet printer used to practice the present invention.
FIG. 4 is another voltage waveform used in another embodiment of the present invention.
FIG. 4a is yet another waveform used.
FIG. 5 is a circuit diagram showing resistance in series with a longitudinal vibration mode piezoelectric transducer driven by the signal generator of FIG. 3, which uses the various waveforms planned by the present invention.
FIG. 6 shows the resonant frequency and harmonics of the transducer superimposed on the drive waveform to obtain high speed droplets with long range.
BEST MODE FOR CARRYING OUT THE INVENTION Referring to FIG. 2A, a voltage drive waveform of a piezoelectric transducer in one embodiment of the present invention is shown. After time A, a pulse 23 is generated between time B and time C and applied to the piezoelectric transducer, which further contracts the piezoelectric transducer as shown in FIGS. 1B and 1C. Let However, unlike the prior art voltage waveform of FIG. 1A, another short pulse that begins at time E and ends at time F immediately follows pulse 23. According to the present invention, the pulse between time B and time C causes piezoelectric resonance vibration, while another short pulse between time E and time F causes harmonic vibration of the piezoelectric transducer. The harmonic vibration has a high acceleration component and an amplitude sufficient to prevent the tail from forming as in the prior art shown in FIG. 1F as described below with reference to FIGS. 2B and 2C.
As shown in FIG. 2B, a drop between time B and time C causes a droplet connected to ink 12 in chamber 14 to exit out of orifice 16 similar to the prior art orifice shown in FIG. 1E. Pressed. However, the short pulse 25 between time E and time F shown in FIG. 2A causes harmonics of the piezoelectric resonance vibration and prevents the narrow tail from being formed from the band 22 as shown in FIG. 2B. As shown in FIG. 2C, it produces a substantially spherical droplet 20 having a short tail 22 compared to the elongated tail 22 shown in FIG. 1F.
In the present invention, the piezoelectric transducer 10 is selected because it has a high resonance frequency. The resonance frequency of the piezoelectric transducer 10 exceeds 50 kHz, preferably 75 kHz or more, more preferably 90 to 300 kHz, and represents a preferred embodiment. The harmonic frequency caused by the following pulse between time E and time F exceeds 150 kHz, and preferably exceeds 200 kHz, and in the preferred embodiment 235 kHz is used. In the preferred embodiment, the resonant frequency is 90-300 kHz and the harmonic is 235-800 kHz, so the pulse 23 between time B and time C is preferably 14.5 microseconds, A pulse pulls the ink black in the meniscus 18 to the position shown in prior art FIG. 1C. A pulse 23 between time B and time C is followed by a dead time of preferably 1.5 microseconds between time C and time E, followed by time E and time E to generate a harmonic of 235 kHz. A short pulse of 3.0 microseconds in width with time F follows. The harmonic resonance with a frequency of 235 kHz creates a pressure wave with a high acceleration component, and this pressure wave disturbs the ink flow in the orifice when the ink flows out as described above. As a result, tail formation is greatly affected, and the tail is disconnected from the meniscus 18 much earlier than the conventional method utilizing a single pulse. The surface tension of the liquid here is large enough to keep the droplets together and to accelerate the short tail to a speed equal to the velocity of the droplet head, so that the short tail 22 travels with the droplet 20 head. Can do.
According to another important feature of the present invention, the range of the droplet is improved by increasing the liquid resonance frequency. For example, when the liquid resonance frequency or Helmholtz frequency is increased from 45 kHz to 90 kHz, and the excitation natural frequency of the piezoelectric transducer is increased from 45 kHz to 90 kHz correspondingly, the head advances in 6.5 milliseconds. In this state, the velocity of the droplet tail increases from 4.5 milliseconds to 5.5 milliseconds, and the droplet range increases by at least 75 percent. For example, by applying another pulse with a short width to cause harmonic resonance oscillation at 235 kHz, the tail of the droplet is cut off fast enough to increase the tail speed to 6.5-7 meters per second. This increases the range of the ink droplets by approximately 200 percent.
It is clear that a short pulse can be used before or after a long pulse to cause the same harmonic oscillation to quickly break the droplet and shorten the tail. As shown in FIG. 2A ′, a short pulse 27 is generated between time G and time H before a long pulse between time B and time C. As a result, the short pulse 27 that follows the long pulse 23 has the same effect because it can cause harmonic frequencies above 150 kHz, in the preferred embodiment, as high as 235 kHz.
FIG. 3 shows a system having a plurality of fluidic devices or jetting devices of the type shown in FIGS. 2B and 2C, in which the orifice 16 shown enlarged in FIG. . The head 24 is driven by a single signal generator 26 connected to a power supply 28 and a voltage regulator 30. A timing circuit 32 is connected to the signal generator to generate a driving voltage pulse in a piezoelectric transducer of a fluid ejection device or ink ejection device incorporated in the head 24. The head 24 is connected to a long pulse of the type described above and its With a short pulse before or after.
As shown in FIG. 3, the droplets 20 are ejected in the direction indicated by the arrow 34 toward the target or object 36 conveyed by the conveyor 38. In many applications, it may be desirable or necessary to move the head 24 slightly away from the target 36. It is therefore important to obtain droplets with high resolution and high speed droplets with long range and little or no tail in order to obtain accuracy according to the present invention.
Obviously, the present invention is not limited to a particular type of waveform. The waveform need not be square or rectangular, but may be serrated as shown in FIG. 4, and the voltage between the long pulse 37 and the short pulse 39 need not be zero and is substantially long and short. The amplitude may be smaller than the highest point of the pulse. In this regard, the long pulse between time I and time J shown in FIG. 4 is approximately triangular, as is the short pulse 39 between time K and time L. Furthermore, the time between time J and time K separating the long and short pulses is characterized by a non-zero voltage that varies like the voltage following the short pulse between time K and time L. There is. The effect is that a long pulse between time I and time J causes an excitation natural vibration or resonance vibration of the piezoelectric transducer, and a short pulse between time K and time L causes a harmonic frequency. Of course, as described above, the short pulse may be before or after the long pulse having the waveform shown in FIG. FIG. 4a shows another pulse 37a and 37b, where a short pulse follows a long pulse.
As mentioned above, the preferred embodiment using the waveforms of FIGS. 2A, 2A ′, 4 and 4A has a long pulse of 14.5 microseconds and a short pulse of 3.0 microseconds. Other embodiments may have different widths depending on the resonant frequency of the piezoelectric transducer. For example, a long pulse may be 5 microseconds to 100 microseconds, and a short pulse may be 0.5 microseconds to 6 microseconds. Similarly, the time between pulses can also vary between 0.1 microseconds and 5 microseconds.
Referring to FIG. 4, it is desirable that the waveform described here can obtain particularly stable performance. In order to obtain the waveform of FIG. 4, it is desirable to have a resistor in series with the piezoelectric transducer. Referring to FIG. 5 in this regard, at least a 100 ohm resistor 40 is connected in series with the piezoelectric transducer 10 disposed between the electrode 42 and the electrode 44. As shown in the figure, the piezoelectric transducer 10 is a longitudinal vibration mode transducer that expands and contracts as shown in FIGS. 2B and 2C, and the length of the piezoelectric transducer 10 is 15 mm (0.6 mm). Inches) or less. The piezoelectric transducer 10 is connected to the chamber 14 via a diaphragm 46. An inflow hole 48 leading into the chamber 14 is shown. In a preferred embodiment, the chamber 14 has a volume small enough to ensure a Helmholtz resonant frequency of 50 kHz or higher, preferably 90 kHz, which chamber 14 March 25, 1997. It has been implemented in the printhead shown in filed US patent application Ser. No. 08 / 828,758, which is incorporated herein by reference. Further details regarding the special impulse ink ejection shown in FIG. 5 are described in US Pat. No. 4,697,193, which forms a part of this application with reference to Helmholtz frequencies above 50 kHz disclosed in this patent. It has not been.
In FIG. 6, a voltage waveform similar to the voltage waveform shown in FIG. 4A is shown superimposed on the chamber pressure of the fluid ejection device shown in FIGS. 2B and 2C. Here, the change in chamber pressure corresponding to the resonant frequency of the device is basically a damped sine that is the result of a long pulse 37b, which is a small wave that is the result of a short pulse 39b that causes the harmonics of the device. Accompany. A small wave corresponding to the harmonics of the device is shaped like a step 50, which coincides with the trailing edge 52 of the short pulse 39b, producing a small droplet as shown in FIG. 2C. For this purpose, the tail of the droplet is cut off. As a result, the droplets can travel further at high speed, i.e. the range is increased.
It is clear that transducer harmonics must be caused to accelerate the droplet tail and ensure that this tail is not decelerated. To illustrate the proper relationship between the resonant frequency and harmonics of a piezoelectric transducer, referring to FIG. 6, the resonant frequency is generally indicated by a sinusoidal shape 48 and the harmonic frequency is indicated by a sinusoidal waveform 50. As shown, this sinusoidal waveform 50 is appropriately spaced with the timing of the pulses such that specific harmonic oscillations occur. This relationship between the harmonic frequency and the resonant frequency ensures that the tail is cut off and that the rest of the tail that stays in the droplet is accelerated to the droplet head, thus reducing the range and speed. Improved. Although a particular transducer and a particular waveform have been shown, it is clear that the present invention may be implemented in a variety of devices including a bubble jet where fluid or ink acts as a transducer. In addition, the present invention may be implemented with transducers of other shapes and forms, i.e. not necessarily in an inflatable transducer in longitudinal vibration mode. For example, a plurality of benders and a plurality of converters sharing a wall may be used. Furthermore, the particular drive waveform may be an energy pulse rather than a voltage pulse, and the transducer may be activated and deactivated at an appropriate time to ensure that a resonant frequency occurs as well as the harmonics. Finally, the fluid need not be ink, but may be fluid that must be ejected in droplets for various purposes such as metering.

Claims (1)

A method of operating an impulse fluid ejection device comprising a chamber, an orifice for ejecting droplets from the chamber, and a transducer having a resonant frequency and a harmonic frequency comprising:
Applying an energy pulse of a first width to the transducer to cause the transducer to oscillate at a resonant frequency, and in response to the resonant frequency, the head is coupled to the head. Ejecting a droplet having a tail with the tail integral with the liquid in the chamber;
Causing the transducer to generate another energy pulse having a different width and having a different width shorter than the one energy pulse to cause a vibration at a harmonic frequency. ,
The vibration at the harmonic frequency causes a pressure wave to flow in the liquid in the chamber so that the tail is separated from the liquid in the chamber and the head and tail travel at the same speed toward the target. How to generate.

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